Including the originating PID in every message?

[Markku Savela]

I would find it convenient if the process/task ID of the message
originator would be easily available from every received message.

[Currently, getting PID requires complicated round-trip query, which
I'm not quite sure would work for all types of messages and signals.]

Should I just define a new type of header field (is next free code
currently 9?), with binary uint32 (or uint64) value, and cook up a
patch? Or has anyone done this or equivalent already?

Unfortunately, this would mean that dbus would need to modify every
message that passes through it. As I understand, it currently does
this unmarshal/marshal already for all messages, and thus adding new
field to header would not be much extra... ...but, maybe that will not
be true always in future?